Different sensors for determining the amount, presence, or concentration of substances are well known and widely used within different industries in order to monitor and control physical parameters of a particular environment.
Since different applications require the use of specially designed sensors there is a vast amount of different sensing technologies commercially available.
One such sensing technology involves the use of light, wherein the sensor determines the amount of absorbance and/or transmittance through a sample being arranged in the optical path of the emitted light. Hence, such sensor arrangement typically involves a light source arranged on a first side of the sample, a detector arranged on the opposite side of the sample, and a controller for determining the absorbance and/or transmittance. Preferably, the controller also includes a calculating unit for converting the detected transmittance and/or absorbance into a quantity of the sample, such as the amount of a particular substance within the sample.
Examples of prior art light sensors are described in U.S. Pat. No. 3,895,233 and in EP0762107.
Light sensors are very attractive since they can be used for many different samples. The light absorbance spectrum of a substance is normally a complex curve why significant sensor resolution may be obtained by choosing a specific wavelength of the light used.
In food processing, such as liquid food packaging, carton-based packaging material is folded to a package whereafter it is filled with liquid food product. For complying with national safety regulations, but also to assure the quality of the enclosed food product, it is necessary to assure that the enclosed food product is sterilized. However, sterilization must also be provided for the package itself before being filled and sealed.
In modern filling machines the packaging material is normally sterilized by hydrogen peroxide (H2O2). The sterilization may either occur in a H2O2 sterilization chamber through which the packaging material is transported, or as a spray unit which provides a H2O2 gas into semi-finished packages prior to filling and sealing. Hence, there is a sterile zone through which the packaging material passes before filling.
The light absorbance spectrum of H2O2 has proven to be suitable for light sensors for detecting and measuring the amount of H2O2 in the sterile zone of the filling machine. Such light sensors also require the use of optical lenses and windows in order to direct the light through the H2O2 and to the detector. However, in gaseous environments such as the sterile zone of a liquid food filling machine deposits on the optical components have contributed to an increased noise in the measurements, thus reducing the quality of the measurements.
Although the above described sensor arrangements provide some advantages the complete construction of such sensor arrangement is not suitable in specific applications where interfering material tend to form deposits in the optical path.
Hence, there is a need for an improved sensor arrangement, especially for applications where it is of crucial importance to measure the amount of sterilizing substances within a sample.